JPH10336000A - High-frequency signal switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-frequency signal switch which can obtain sufficient isolation characteristic, with a simple constitution. SOLUTION: A high-frequency signal switch is constituted of a series element, which connects the input and output of the switch to each other and a shunt element which grounds the output terminal of the switch. The shunt element contains a capacitor C1 which resonates with a leakage inductance L1 contained in an FET(field effect transistor) 2 and the shunt element as a whole at the center frequency f2 of a transmission band. At the time of improving the isolation characteristic of the switch, the characteristic can be improved to about -10 dB, by lowering the total impedance of the shunt element which is 8 Ωto 2 Ω, when the impedance of the inductance L1 is canceled by means of the capacitor C1, and when the value of the turning on resistance of the FET 2 is 2 Ω and the impedance of the inductance L1 is 6 Ω.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-frequency signal switch, and more particularly to a high-frequency signal switch for microwave communication.

[0002]

2. Description of the Related Art A conventional high-frequency signal switch, for example, a single-pole single-throw (SPST) switch, has a configuration as shown in the circuit diagram of FIG. That is, it is composed of a series element (mainly a field effect transistor FET1) connected from the input to the output, and a shunt element (mainly the field effect transistor FET2) whose output terminal is grounded.

When the FET1, which is a series element, is turned on and the FET2, which is a shunt element, is turned off via the resistors R1 and R2 of the gate circuit, the input is connected to the output and the high-frequency signal switch is turned on. Similarly FET
When 1 is turned off and FET2 is turned on, the high frequency signal switch is turned off. That is, the FET has an on-resistance of, for example, 2Ω for a DC or low frequency signal.
Since the off-resistance value is extremely high, for example, several MΩ, the characteristics of the signal switch (the isolation between the input and the output when the signal switch is off is -120 MHz) are extremely excellent.

However, high frequency signals such as 1000 MHz
, The impedance of the stray capacitance C0 (for example, 2 pF) between the source and the drain of the FET becomes low, for example, 80Ω, and the impedance of the leakage inductance L2 (for example, 1 nH) inside the shunt element becomes
For example, it becomes 6Ω and cannot be ignored. Therefore, as shown in FIG. 4, the lower limit frequency for transmission is f1 and the center frequency is f1.
2, the upper limit frequency is f3, and the center frequency f2 is 1
When the frequency is set to 000 MHz, the isolation at f2 is about -20 dB.

For example, if the required performance requires that the isolation at the time of off is -30 dB or more, there is a problem that the required performance cannot be satisfied.

Japanese Patent Application Laid-Open No. Hei 5-29995 discloses FIG.
A high-frequency signal switcher composed of a series element (resonant circuit) 1 connected from the input to the output and a shunt element (resonant circuit) 2 whose output terminal is grounded has been proposed.

In FIG. 5, a resonance circuit 1 and a resonance circuit 2 are basically the same two-terminal circuit. When the FETs 3, 4 or the FETs 5, 6 are turned on, the capacitor C2 or C3 is used.
And the inductor L3 or L5 constitute a parallel resonance circuit, and provide high impedance between the two terminals. FET3,
When 4 or FETs 5 and 6 are off, a series resonance circuit is formed by capacitor C2 or C3 and inductor L4 or L6, and a low impedance is applied between the two terminals.

Therefore, when the resonance circuit 1 is set to a high impedance state and the resonance circuit 2 is set to a low impedance state,
When the high-frequency signal switch is turned off, the resonance circuit 1 is set to a low impedance state, and the resonance circuit 2 is set to a high impedance state, the high-frequency signal switch is turned on.

Assuming that the lower limit frequency for transmission is f1 ', the center frequency is f2', and the upper limit frequency is f3 ', the isolation characteristic in this case is shown in FIG.
(B).

[0010]

Problems to be Solved by the Invention
In the case of the proposal described in Japanese Patent Laid-Open No. 5 (1993) -1995, for example, the capacitance value of the capacitor C2,3 is the stray capacitance C0 between the source / drain of the FET.
(See FIG. 3). If they are at the same level, it cannot be considered as a simple series / parallel resonance circuit, and will have complicated resonance characteristics, and sufficient high frequency signal switching characteristics cannot be obtained. As the capacitance value of the capacitors C2,3 increases, it is necessary to reduce the values of the inductors L3,4,5,6 accordingly.
It is practically impossible to make it extremely small (less than the inductance of the lead).
There is a problem that cannot be applied to a high-frequency signal switch of a high frequency such as MHz.

An object of the present invention is to provide a high-frequency signal switch which can obtain sufficient isolation characteristics with a simple configuration.

[0012]

A high-frequency signal switch according to the present invention comprises a series element mainly composed of a first switching element connecting an input and an output, and a second switching element connecting the output and a ground. A high-frequency signal switch including a shunt element mainly comprising: an opening / closing control means for controlling opening / closing of the first and second opening / closing elements in a complementary manner; and a shunt element inserted in series with the shunt element. And a capacitor for canceling leakage inductance.

Further, the first and second switching elements are constituted by field effect transistors, and the capacitor is selected to have a value that resonates with the leakage inductance near the center of a transmission band.

The operation of the present invention is as follows. A capacitor is added to eliminate the leakage inductance included in the shunt element in the form of series resonance.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of a high-frequency signal switch according to the present invention, and portions equivalent to those in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, a high-frequency signal switch according to the present invention includes a series element (mainly a field effect transistor FET1) connected from an input to an output, and a shunt element (also a field effect transistor) whose output terminal is grounded. FET2). The series element is FET1 and the stray capacitance C0 between its source and drain.
And inserted into the gate circuit of FET1, through which F
And a resistor R1 for voltage controlling ET1.

The shunt element is FET2 and its source /
A stray capacitance C0 between the drain, a resistor R2 inserted into the gate circuit of the FET2 and controlling the voltage of the FET2 therethrough, and a leakage inductance L1 including the entire shunt element (in the figure, inserted between the capacitor C1 and the ground. Although it is drawn as if it were, this is a temporary drawing,
Exists in a form distributed over the entire shunt element), the inductance L1 and the center frequency f2 of the transmission band, for example, 100
And a capacitor C1 that resonates at 0 MHz.

The operation of the embodiment of the present invention is as follows.
The isolation characteristic shown in FIG. 4 is the same as the conventional example shown in FIG.
In order to improve B, it is necessary to reduce the impedance of the shunt element to about 1/3 (-10 dB).

Assuming that the on-resistance value of FET2 is, for example, 2Ω and the impedance of leakage inductance L1 is 6Ω, when the impedance of inductance L1 is canceled out by capacitor C1, about 7 (2 + 6; vector sum)
By lowering the total impedance of the shunt element which has changed from Ω to 2 Ω, as shown in FIG.
It can be improved by about dB. The insertion loss characteristics in this case are shown in FIG.

Further, even if the capacitor C1 is inserted, it is important not to increase the inductance L1 as much as possible.
Use a feedthrough capacitor (very small ground inductance) as the capacitor C1 and keep it as short as possible (in the case of wire bonding, use as many wires as possible)
Must be connected to FET2.

[0022]

As described above, the present invention has the effect of improving the isolation characteristic by about -10 dB near the center frequency of the transmission band by canceling the impedance of the leakage inductance of the shunt element by the capacitor. is there.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an isolation characteristic and an insertion loss characteristic of an example of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional high-frequency signal switch.

FIG. 4 is an explanatory diagram of an isolation characteristic of an example of a conventional high-frequency signal switch.

FIG. 5 is a circuit diagram showing another example of a conventional high-frequency signal switch.

FIG. 6 is an explanatory diagram of an isolation characteristic and an insertion loss characteristic of another example of the conventional high-frequency signal switch.

[Explanation of symbols]

 FET1, FET2 Field-effect transistor C1 Capacitor L1 Leakage inductance 1, R2 Resistor

Claims (3)

[Claims] 1. A high-frequency signal switch including a series element mainly composed of a first switching element connecting an input and an output, and a shunt element mainly composed of a second switching element connecting the output and the ground. An open / close control means for controlling opening / closing of the first and second switching elements in a complementary manner, and a capacitor inserted in series with the shunt element to cancel a leakage inductance included in the shunt element. High-frequency signal switcher. 2. The device according to claim 1, wherein said first and second switching elements are formed by field effect transistors.
The high-frequency signal switch according to the above. 3. The high-frequency signal switch according to claim 1, wherein the capacitor is selected to have a value that resonates with the leakage inductance near the center of the transmission band.